Helicopter manufacturers are continually expanding the envelope of helicopter technology so that they can offer the most operationally effective, cost efficient helicopters to their customers. Due to the enormous costs involved in bringing a new helicopter which incorporates the latest state of the art technology to market, the introduction of a new helicopter to the market by a given manufacturer is a relatively unique occasion. In addition to the high costs involved, the delivery cycle for a new helicopter, from conception to the production model, encompasses many years, which further militates against the frequent introduction of new helicopter models.
As an alternative to marketing new helicopters that incorporate state of the art technology, many helicopter manufacturers offer upgrades of basic helicopter production models, i.e., derivative models. Such derivative models may offer new or enhanced operational capabilities, improved performance, increased reliability, and/or lower maintenance requirements by selectively incorporating state of the art technology into the basic helicopter production model to produce the derivative model. By retaining most of the constituent elements of the basic model, delivery costs of the derivative model are generally not significantly greater than the basic production model. The delivery cycle for a derivative model, moreover, may be relatively inconsequential since production derivative models may be segued into the basic model production line in parallel with, or as an alternative to, the basic production model.
The alternative approach, more importantly, may provide an additional benefit to the helicopter manufacturer. The state of the art technology selectively incorporated into the basic helicopter production model to produce the derivative model may also provide the basis for retrofitting existing basic helicopter production models. Retrofits of basic helicopter production models, in addition to providing a new revenue stream for the helicopter manufacturer, allows the customer to upgrade the basic helicopter production model(s) to the more operationally effective derivative model.
One approach to providing a derivative model that is particularly appealing is the incorporation of an augmented engine system, i.e., a powerplant system having a greater horsepower output, in a basic production model. The greater horsepower output of an augmented powerplant system may significantly enhance the operational effectiveness of the derivative model, and may provide the derivative model with an expanded mission capability. In addition, the augmented powerplant system provides the flexibility for incorporating further state of the art technology in the derivative model, e.g., the augmented powerplant system may be configured to provide additional power for the accessory modules.
However, to incorporate an augmented powerplant system in a basic helicopter production model may require a significant redesign of the baseline powertrain system to accommodate the higher torque output of the augmented powerplant system. Such a redesign effort would include such modifications as changes in the reduction ratio(s) of the powertrain system to accommodate the increased torque output of the augmented powerplant system, changes in the airframe/powerplant structural interfaces, relocation of the engine input/gimbal mounting sites, relocation of the power take-off sites for accessory subsystems, relocation of the take-off site for the tail rotor power subsystem, expansion of the structural envelope, i.e., the radial and/or height dimensions, of the main transmission gearbox housing to accommodate configurational changes in the powertrain system, which would perforce, change the mounting sites, i.e., feet, of the gearbox housing. While structural and/or functional redesign of the basic helicopter production model, and in particular, the baseline powertrain system, is one approach to incorporating an augmented powerplant system in helicopter derivative models, such a course of action incurs increased expense in redesign efforts and delays in providing a finished product for marketing efforts.
In addition, such redesign efforts pragmatically eliminate the retrofitting of augmented powerplant systems in the helicopter manufacturer's existing baseline production models. While the cost and time expenditures may be acceptable in manufacturing derivative models for first sales, such cost and time expenditures may prove unacceptable for the retrofit scenario. In addition to the cost and time expenditures required to modify the basic production model to accommodate the augmented powerplant system, it will be appreciated that the owner of the basic production model being retrofitted also incurs additional expenses in the form of lost revenues while the basic production model is out of service for retrofit.
A need exists to provide an upgraded powertrain system having a sufficient degree of commonality with a baseline powertrain system such that the upgraded powertrain system is retrofittable in a basic helicopter production model that incorporates or is retrofitted with an augmented powerplant system. The upgraded powertrain system should be configured for maximal commonality with the baseline powertrain system of existing helicopter production models to minimize redesign modifications and/or to facilitate incorporation/retrofit in basic helicopter production models to provide derivative models at reasonable costs in a short period of time. The upgraded powertrain system should include a stacked compound planetary gear train having staggered, biplanar primary planetary pinions wherein the stacked compound planetary gear train provides an increased reduction ratio to accommodate the increased horsepower output of the augmented powerplant system while concomitantly providing a baseline RPM output to the main rotor shaft.